Method and apparatus for dispersing glomerate particles



March 8, 1966 c. R. PETERSON 3,239,717

METHOD AND APPARATUS FOR DISPERSiNG GLOMERAIE PARTICLES Filed Feb. 26,1962 United States Patent 0 3,239,717 METHOD AND APPARATUS FOR DISPERSING GLOMERATE PARTICLES Carl R. Peterson, Lexington, Mass, assignor toGoodrich- High Voltage Astronautics, Inc., Burlington, Mass, acorporation of Delaware Filed Feb. 26, 1962, Ser. No. 175,458 6 Claims.(Cl. 3173) This invention relates to the generation of a dispersivespray from a powdered substance, and to the breaking up of theagglomerated groups into which the consitituent particles of such apowdered substance tend to form. More particularly, it comprehendsinserting an electrically conductive or semi-conductive powderedsubstance between two electrostatically charged plate members Whereinthe particles are successively attracted from one plate member to theother. The continuing series of impacts as the particles impinge firston one plate member and then on the other eifectively break up anyagglomerated groups existing in the powdered substance. The oscillatingparticles are then concentrated at the center of the plate members bythe slightly inclining adjacent surfaces thereof, and an aperturescentrally disposed in one of said plate members provides means forejecting a spray of such particles.

The principles of my invention are applicable to any type of dust feedapparatus and will find extensive use especially in instances where thepowdered particles are small, three microns and less, and where gooddensity uniformity is required. Many chemical applications, as well ascolloid propulsion devices and the like are typical examples. A morespecific example of the utility of such a device is that of drysubstance spray printing. In a system for automatically sorting lettersin accordance with certain symbols marked thereon, it is required thatsuch symbols be put on the letters without the use of pressure. Also,since the sorting machine pick up apparatus is responsive to light, andread out is relatively critical, it is important that the consistency ofthe symbol be uniform. The present invention discloses apparatus that isadapted to effectively meet these requirements. In combination with aproper stencil any symbol may be uniformly sprayed on a letterregardless of the surface texture or thickness thereof. The reliabilityand uniformity of symbols marked by such a dry spray stencilingprocedure, then, make it preferable to stamping or liquid spraytechniques.

The state of the art prior to my invention is reflected by devices whichmechanically agitate the particles and eject the desired spray by meansof an aspirator nozzle. Mechanical agitation of dust or powder comprisedof particles of three microns or less is particularly ineffective, andit is in this range that my invention finds its widest application.Another current method of providing a powdered spray comprehendsdispersing a finely divided solid by means of gas under pressure. Thismethod, of course, does not solve the agglomeration problem andtherefore does not produce a spray of uniform density.

Accordingly, it is a principal object of my invention to provide a newand improved method for dispersing, in a finely divided powdersubstance, the glomerate particles that form therein.

It is another object of my invention to provide novel dust feedapparatus adapted to generate a spray of finely divided particles, saidspray having better density uniformity than has heretofore been obtainedby like devices.

It is still another object of my invention to provide electrostaticmeans for breaking up the glomerate particle groups into which a finelydivided powder substance tends to form.

It is yet another object of my invention to provide apparatus of thetype described whereby a powdered substance consisting of particles ofless than three microns may be effectively de-agglomerated and ejectedin the form of a spray or jet.

These, together with other objects and advantages of my invention willbecome more apparent from an examination of the following detaileddescription of one pres ently preferred embodiment thereof taken inconjunction with the accompanying drawing wherein:

FIGURE 1 schematically represents the electrostatic plate members of myinvention and their geometric relationship to certain particlesoscillating therebetween; and,

FIGURE 2 is a sectional view of one illustrative embodiment of theapparatus of my invention.

In accordance with the principles of my invention electricallyconductive plate members 13 and 14 are arranged as illustrated inFIGURE 1. A voltage, preferably DC, is applied therebetween that issuflicicnt to provide a voltage gradient in the order of 10 kv./cm. atthe center of said plate members. A supply of electrically conductive orsemi-conductive powdered substance 6 is supplied between the platemembers by a plunger 5.. The particles of powdered substance 6 tend toadhere together and form glomerate groups 16. The usual application ofthe present device comprehends a powdered substance whose constituentparticles are of 3 microns or less. For the purpose of illustration,however, the particles of FIGURE 1 have been made disproportionallylarge. The dust particles and glomerate groups then, upon contact withplate member 14 become electrically charged to the same polarity as theplate member itself. That is, in the present illustration, they becomeinitially positively charged. Because of the proximity of negativelycharged plate member 13 and the voltage gradient between plates, thepositively charged particles and glomerate groups are attracted fromplate member 14 to plate member 13. Upon reaching plate member 13 theparticles and glomerate groups lose their positive charge and becomenegatively charged. The process is then repeated and the particles andglomerate groups are attracted back to the positive plate. Because platemember 14 is inclined with respect to plate member 13, the particles asthey travel from plate to plate continually move toward the center ofthe plates as indicated by arrows 17 and finally escape through aperture10. The particles, as they impinge first off one plate member and thenthe other, do so with some force and after a number of such collisionsall the glomerate groups are broken up into original particles.Consequently the spray, asv it issues from aperture 10 consists ofindividual particles 18.

Referring now to FIGURE 2, there is illustrated a sectional view of onepresently preferred embodiment of my invention. The plate members 13, 14thereof are fabricated of electrically conductive material such ascopper and have adjacent face sections 3, 4 arranged to cause particlesoscillating therebetween to concentrate at aperture 10. This is done bygrinding face section 4 to a recessed conic geometry, as illustrated,having its apex opposite aperture 10. Annular ridges 11, 12 are providedto prevent the escape of excessive amounts of the powdered substancebetween the edges of plate members 13, 14. Insulating member 7 maintainsa sufiicient distance between plate members to prevent any dischargethereacross. A voltage sutficient to maintain operation of the device,in the present illustration 2500 kv., is supplied from voltage source 8.A supply of powdered substance 6 is provided by means of plunger 5. Thesignificant dimensions of the present illustrative example are; the 2.5inch diameter of face sections 3, 4; the .01 inch diameter of aperture10; and the .2 inch distance between apex 15 and aperture 10. Suchdimensions are not controlling,

3 however, and are cited merely to indicate relative proportions of theapparatus. Various factors such as size of particle, voltage,application of the spray, capacity of the apparatus, and whether or notthe device is used in a vacuum, will, of course, determine the exactdesign and dimensions of any given device. Finally, the apparatusillustrated in FIGURE 2 is packaged in and insulated from a housingmember (not shown).

There has thus been disclosed a novel method and apparatus whereby theseveral objects of my invention are accomplished. While specificstructure has been described by Way of illustrating said invention, itis not intended that any limitation of scope or concept by impliedtherefrom, the full extent of the invention being defined in theappended claims.

I claim:

1. The method of breaking up a quantity of agglomer ated electricallyconductive particles in a spray apparatus comprising the step ofinjecting said quantity of agglomerated electrically conductiveparticles between two electrostatically charged plates of opposite, D.C.polarity whereby the particles dwell between said plates and come inrepeated contact with said plates alternately, such particles assuming,upon such contact, and electrostatic charge of the same polarity as thatof the contacted plate so that they are repelled by said platesalternately upon contact therewith.

2. Apparatus for producing a disperive spray from a quantity ofagglomerated electrically conductive particles comprising twoelectrostatically charged plate members spaced apart in condenserrelationship, one of said plate members having an aperture therein, theadjacent surfaces of said plate members being inclined toward oneanother in such a manner as to deflect particles traversing the spacetherebetween through said aperture, and means for injecting between saidplate members said quantity of agglomerated conductive particles.

3. Apparatus for producing a dispersive spray from a quantity ofagglomerated electrically conductive particles comprising first andsecond metallic plate members, said first plate member having at leastone plane surface and including an aperture centrally disposed therein,said second plate member having one recessed conic surface, said conicsurface of said second plate member being proximate and adjacent to saidplane surface of said first plate member, the apex of said conic surfacebeing opposite said aperture, means for applying an electrical potentialbetween said plate members, and means for injecting between said platemembers said quantity of agglomerated conductive particles.

4. The method of claim 1 for breaking up a quantity of agglomeratedelectrically semi-conductive particles.

5. Apparatus as defined in claim 2 for producing a dispersive spray froma quantity of agglomerated electrically semi-conductive particles.

6. Apparatus as defined in claim 3 for producing a dispersive spray froma quantity of agglomerated electrically semi-conductive particles.

References Cited by the Examiner UNITED STATES PATENTS 1,475,995 12/1923Heis et al. 317-262 1,832,096 11/1931 Chafiee et al. 3l7-262 2,628,7852/1953 Fink 241-1 2,896,263 7/1959 Frederick et al. 317-262 XR SAMUELBERNSTEIN, Primary Examiner.

1. THE METHOD OF BREAKING UP A QUANTITY O AGGLOMERATED ELECTRICALLY CONDUCTIVE PARTICLES IN A SPRAY APPARATUS COMPRISING THE STEP OF INJECTING SAID QUANTITY OF AGGLOMERATED ELECTRICALY CONDUCTIVE PARTICLES BETWEEN TWO ELECTROSTATICALLY CHARGED PLATED OF OPPOSITE, D.C. POLARITY WHEREBY THE PARTICLES DWELL BETWEEN SAID PLATES AND COME IN REPEATED CONTACT WITH SAID PLATES ALTERNATELY, SUCH PARTICLES ASSUMING UPON SUCH CONTACT, AND ELECTROSTATIC CHARGE OF THE SAME POLARITY AS THAT OF THE CONTACTED PLATE SO THAT THEY ARE REPELLED BY SAID PLATED ALTERNATELY UPON CONTACT THEREWITH. 